How to Calculate Your Flight Carbon Footprint

Aviation accounts for roughly 2.5% of global CO2 emissions, but for frequent flyers the personal share is much higher. Knowing your flight carbon footprint is the first step toward more conscious travel decisions. This guide explains how flight emissions are estimated, which factors matter most, and what you can do to reduce your impact.

The Basics: How Flight Emissions Are Calculated

Flight carbon emissions depend on several factors, but the core formula is simple:

CO2 (kg) = Distance (km) x Emission Factor (kg CO2 per passenger-km) x Class Multiplier

The emission factor depends on the length of the flight because takeoff and climb are the most fuel-intensive phases. Short-haul flights burn more fuel per kilometer than long-haul flights, since takeoff and climb make up a larger share of a short journey.

The DEFRA Methodology

One of the most widely used sources for flight emission factors is the UK government’s greenhouse gas conversion factors, often called the DEFRA factors and now published every year by the Department for Energy Security and Net Zero (DESNZ). The factors take into account:

• Flight distance category: the factors separate domestic, short-haul and long-haul flights to and from the UK, plus international flights between other countries, because fuel burn per kilometer changes with distance.
• Radiative forcing: the factors are published with and without the extra warming effect of emissions at altitude (contrails, NOx). Results differ by a large margin depending on which version a calculator uses.
• Average passenger load: the factors assume typical occupancy rates for commercial flights.
• Fuel burn per passenger-km: based on fleet averages that mix modern and older aircraft.

FlightLog uses per-kilometer factors based on the DEFRA figures, adjusted by cabin class, to estimate the carbon footprint of every flight you log. It is an estimate based on distance and class, not a measurement of the actual fuel burned on your flight.

How Cabin Class Affects Your Footprint

Your cabin has a large effect on the footprint of your seat. Business and First seats take up more floor space, so fewer passengers share the fuel burn of the aircraft. Typical long-haul multipliers, relative to Economy, are:

On a long-haul flight, a First class seat can account for four times the CO2 of an Economy seat on the same aircraft. The exact multipliers vary with the length of the flight (on short-haul flights, the same factors count a Business seat as 1.5 times an Economy seat), and airlines configure their cabins differently.

Putting Numbers in Perspective

Raw kilograms of CO2 are hard to picture, so equivalences help. Two commonly used ones:

• Trees: a mature tree is commonly said to absorb about 22 kg of CO2 per year.
• Car kilometers: the same UK factors put an average car (fuel type unknown) at about 167 g of CO2e per kilometer.

For example, a round-trip Economy flight between Paris and New York is roughly 1,300 kg of CO2e per passenger when estimated with these factors, radiative forcing included. That is about the same as driving an average car for 7,800 km, or the yearly absorption commonly attributed to about 59 trees. Calculators that count only CO2 from fuel give lower figures, so always compare numbers from the same method.

Practical Tips to Reduce Your Flight Emissions

1. Choose direct flights

Takeoff and climb use the most fuel, and a connection adds a second takeoff and often a longer route. A nonstop flight over the same distance usually produces less CO2 than a connecting itinerary, so prefer nonstop options when the price difference is small.

2. Mind your cabin class

As the table above shows, cabin class changes your personal footprint a lot. A Business seat on a long-haul flight counts for 2.9 times the CO2 of an Economy seat on the same flight.

3. Prefer newer aircraft

Newer aircraft such as the Airbus A350 and Boeing 787 were designed to use around 20-25% less fuel than the generation they replace, according to their manufacturers. Airlines often show the aircraft type when you book. In FlightLog, each flight can carry its aircraft type and registration, and the aircraft collection unlocks a card for the types you have flown.

4. Consider the train for short distances

On routes of a few hundred kilometers where a high-speed train exists, such as Paris to London, the train typically emits a small fraction of the CO2 of the equivalent flight.

5. Track what you fly

You cannot reduce what you do not measure. FlightLog shows the carbon estimate of each flight and your statistics year by year, so you can see how your flying changes over time.

Start Tracking Your Carbon Footprint

FlightLog estimates the carbon footprint of every flight with factors based on the DEFRA figures, by cabin class. To fill your history quickly, scan your boarding passes, import a photo of a booking confirmation, or import your flights from another app. Download FlightLog for free and see your impact from your first flight.